The LCDs (Liquid Crystal Display) can be constructed in a relatively compact size due to the rapid advance of TFT (Thin Film Transistor) or LTPS (Low Temperature Poly-Silicon) technique in addition to its lower power consumption and low radiation. The manufacturers worldwide have devoted themselves to further research and thus improve the materials, processes and equipments. The qualities of the LCD are accordingly and largely promoted while the cost goes down day-by-day, which, in turn causes a wide use of the LCD system at homes and offices. Note that the LCD itself is not a light emitting instrument, and requires a backlight module in order to display images and information on the display panel. Good or bad quality of the LCD system can directly affect pixel pitch of the backlight module. The backlight module is therefore an important component in the LCD system.
Referring to FIG. 1, an exploded view of a prior art backlight module is shown to include an upper prism 10, a lower prism 11, a diffuser 12, a light guide 13, a plastic frame 14 and a reflection sheet 15. Generally, a light source (not shown) is provided at one edge of the light guide 13 in the edge light form so as to emit light beams into the light guide 13. The light beams emitted from the light source pass through the light guide 13, and then reflects from an upper surface to another direction. The plastic frame 14 is disposed behind the light guide 13 in order to prevent diffusion of light beams from a lower surface of the light guide 13 so that the diffused light beams can hit back the light guide 13, thereby increasing the utilization of the light beams. An optical film unit consisting of the diffuser 12, the lower prism 11 and the upper prism 10, is disposed on the light guide 13 in order to enhance the brightness of the display panel uniformly.
The aforesaid upper and lower prisms 10,11 are commonly known as BEF (brightness enhanced film), and are used mainly for enhancing focusing effect. Alternately, optical polarizers can be used for providing the same focusing effect. The diffuser 12 above the light guide 13 is used for diffusing uniformly and tenderly the light beams passing through the light guide 13.
In order to enhance the transmission, brightness and reflection of light beams from the upper and lower surfaces of the light guide 13, a plurality of pattern or V-groove (V-cut) structures are fabricated on the upper and lower surfaces by screen printing technique such that the light beams can diffuse and reflect therefrom. Referring to FIGS. 2A and 2B, the light guide 13 of the prior art backlight module 1 is shown to have dot patterns 131, wherein the dots in FIG. 2A are fabricated in parallel rows in such a manner that the dot distant from a light incident side of the light guide 13 has a larger dimension than the dot adjacent to the light incident side of the light guide 13 so as to increase the light reflection effect. In FIG. 2B, the dot in one of the specific row is offset from a nearby dot of an adjacent row, and the dots in the row adjacent to the light incident side of the light guide 13 are sparsely distributed while the dots in the row distant from the light incident side thereof are densely distributed. FIG. 2C is a side view of the light guide 13, illustrating how the dots are distributed on the lower surface thereof for light reflection therefrom.
In addition to the dot patterns, FIG. 3A shows side view in which, the lower surface of the light guide 13 in the prior art backlight module is formed with a plurality of V-cuts 132 in order to achieve the same effect. FIGS. 3B and 3C respectively show bottom views, illustrating distributions of V-cuts 132, wherein the cuts 132 in FIG. 3B are shown in parallel rows while the cuts 132 in FIG. 3C are shown in concentric rows.
Though the distribution of the pattern or V-cuts of specific patterns on the light guide 13 can provide uniform and enhance brightness effect, there are still some disadvantages resulting from the use of the prior backlight module 1. For instance, in order to lower the purchasing cost of and reduce the power consumption of a mobile phone, only a pair of LEDs (Light Emitting Diode) is provided at the light incident side of the light guide 13. Under such arrangement, there may occur uneven distribution of brightness adjacent to the light incident side of the light guide 13, i.e. a section of area immediately adjacent to the LED is brighter than two opposite areas at two sides of said section of area. In the prior art, the entire area adjacent to the light incident side of the light guide 13 is known as Light Transient Area, and the area distant from the LED and having uniform brightness throughout is known as Active Area (AA). In use, the superiority or inferiority of pixel in the display panel heavily depends on degrees of brightness of the Active Area.
Note that the aforesaid arrangement of the pattern or dot patterns on the light guide 13 though provides uniform distribution of light beams, a space of at least 3.2 mm is preserved in front of the prior art backlight module in order that the defected area cannot be seen on the display panel of the LCD system. Under this arrangement, dimension of the Active Area is adversely reduced and limit the space utility of the prior art backlight module.
In the prior art technique, in order to achieve uniform brightness at the Active Area of the light guide 13, the pattern or dot patterns are fabricated continuously in small scale, which, in turn, results in extra manufacture cost. The prior art technique is unable to solve the existing problem.